Most entertainment and information media such as television, radio, newspapers, and magazines are heavily subsidized by advertising. A recently emerging medium is on-line services in which a customer connects to an information service via a computer and telephone line. Many on-line services are subscription-based and require a fee to use. Accordingly, on-line services could be significantly more attractive to customers if the subscription costs could be reduced by advertiser subsidies. Unfortunately, on-line service providers have not yet found a way to deliver advertising in ways that are both effective for advertisers and acceptable to the customer. This is largely because a balance has not been found between consumers' desire to have complete control over their on-line experience (and its cost) and the advertiser's need to deliver its message to the customer. Unlike many traditional information media, an on-line service may charge its customers according the amount of time the customer is connected to the on-line service. Thus, viewing advertising may cost the customer money.